I70 RIO PLATA chap. 



watching some that were suspended by a single thread, 1 

 several times observed that the slightest breath of air bore them 

 away out of sight, in a horizontal line. On another occasion 

 (25th) under similar circumstances, I repeatedly observed the 

 same kind of small spider, either when placed or having crawled 

 on some little eminence, elevate its abdomen, send forth a thread, 

 and then sail away horizontally, but with a rapidity which was 

 quite unaccountable. I thought I could perceive that the spider, 

 before performing the above preparatory steps, connected its 

 legs together with the most delicate threads, but I am not sure 

 whether this observation was correct. 



One day, at St. Fe, I had a better opportunity of observing 

 some similar facts. A spider which was about three-tenths 

 of an inch in length, and which in its general appearance 

 resembled a Citigrade (therefore quite different from the 

 gossamer), while standing on the summit of a post, darted 

 forth four or five threads from its spinners. These, glittering 

 in the sunshine, might be compared to diverging rays of light ; 

 they were not, however, straight, but in undulations like films 

 of silk blown by the wind. They were more than a yard in 

 length, and diverged in an ascending direction from the orifices. 

 The spider then suddenly let go its hold of the post, and was 

 quickly borne out of sight. The day was hot and apparently 

 quite calm ; yet under such circumstances, the atmosphere can 

 never be so tranquil as not to affect a vane so delicate as the 

 thread of a spider's web. If during a warm day we look either 

 at the shadow of any object cast on a bank, or over a level 

 plain at a distant landmark, the effect of an ascending current 

 of heated air is almost always evident : such upward currents, 

 it has been remarked, are also shown by the ascent of soap- 

 bubbles, which will not rise in an indoors room. Hence I 

 think there is not much difficulty in understanding the ascent 

 of the fine lines projected from a spider's spinners, and after- 

 wards of the spider itself ; the divergence of the lines has been 

 attempted to be explained, I believe by Mr. Murray, by their 

 similar electrical condition. The circumstance of spiders of 

 the same species, but of different sexes and ages, being found 

 on several occasions at the distance of many leagues from the 

 land, attached in vast numbers to the lines, renders it probable 

 that the habit of sailing through the air is as characteristiq of 



